GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2004 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L (L26 and L32) 🢒 Powertrain Relay Diagnosis

Circuit Description

The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The powertrain control module (PCM) supplies the ground path to the relay coil control circuit, via an internal integrated circuit, called an output driver module. When the PCM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allow current to flow from the battery to the following fuses:

    • The ETC fuse
    • The ELEK IGN fuse
    • The FUEL INJ fuse
    • The O2 SSR fuse
    • The Emission fuse

When the ignition switch is turned to the OFF position, power is interrupted to the output driver module in the PCM, and the relay electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which interrupts current flow to the fuses.

If the powertrain relay fails to close, the engine will crank, but will not run. The class 2 communications will be available with the use of a scan tool.

The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics and Power Distribution Schematics in Wiring Systems

Connector End View Reference: Powertrain Control Module Connector End Views and Electrical Center Identification Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC P0685 set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Remove the underhood fuse block cover.
  3. Probe the following fuses with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
    4. • ECT Fuse
    • ELEK IGN Fuse
    • FUEL INJ Fuse
    • O2 SSR Fuse
    • EMISSION Fuse

Does the test lamp illuminate on at least one test point of each fuse?

--

Go to Step 4

Go to Step 14

4
  1. Turn OFF the ignition.
  2. Probe both test points of the 10-amp EMISSION Fuse in the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 5

Go to Step 33

5
  1. Turn OFF the ignition.
  2. Remove the powertrain relay from the underhood fuse block with the J 43244 Relay puller Pliers. Refer to Relay Replacement in Wiring Systems.
  3. Probe both test points of the 10-amp EMISSION Fuse in the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 9

Go to Step 6

6
  1. Turn OFF the ignition.

    2. Notice: Refer to Test Probe Notice in the Preface section.

  2. Probe terminal cavity A6 at the underhood fuse block with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 21

7
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  3. Disconnect the electrical connector that contains the powertrain relay coil control circuit from the underhood fuse block.
  4. Disconnect the PCM electrical connector that contains the powertrain relay coil control circuit from the PCM.
  5. Probe the powertrain relay coil control circuit at the PCM electrical connector with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 28

Go to Step 8

8

Test the powertrain relay coil control bus bar circuit in the underhood fuse block for a short to ground. Refer to Circuit Testing in Wiring Systems.

Did you find a condition?

--

Go to Step 32

Go to Step 26

9
  1. Turn OFF the ignition.
  2. Remove the ECT fuse from the underhood fuse block.
  3. Probe both test points at the 10-amp EMISSION fuse with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 10

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

10
  1. Turn OFF the ignition.
  2. Remove the ELEK IGN fuse from the underhood fuse block.
  3. Probe both test points at the 10-amp EMISSION fuse with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 11

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

11
  1. Turn OFF the ignition.
  2. Remove the FUEL INJ fuse from the underhood fuse block.
  3. Probe both test points at the 10-amp EMISSION fuse with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 12

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

12
  1. Turn OFF the ignition.
  2. Remove the O2 SSR fuse from the underhood fuse block.
  3. Probe both test points at the 10-amp EMISSION fuse with a test lamp that is connected to a good ground.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 13

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

13
  1. Turn OFF the ignition.
  2. Remove the EMISSION fuse from the underhood fuse block.

    3. Notice: Refer to Test Probe Notice in the Preface section.

  3. Probe terminal A6 at the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 32

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

14
  1. Turn OFF the ignition.
  2. Remove the powertrain relay from the underhood fuse block with a J 43244 . Refer to Relay Replacement in Wiring Systems.

    3. Notice: Refer to Test Probe Notice in the Preface section.

  3. Probe terminal C6 at the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 15

Go to Step 19

15
  1. Turn OFF the ignition.
  2. Probe terminal C5 at the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 19

16
  1. Turn ON the ignition, with the engine OFF.
  2. Probe terminal cavity A6 at the underhood fuse block with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 20

Go to Step 17

17
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  3. Disconnect the electrical connector that contains the powertrain relay coil control circuit from the underhood fuse block.
  4. Disconnect the PCM electrical connector that contains the powertrain relay coil control circuit from the PCM.
  5. Measure the resistance of the powertrain relay coil control circuit with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure greater than the specified value?

5 ohms

Go to Step 29

Go to Step 18

18

Test the underhood fuse block powertrain relay coil control bus bar circuit for a high resistance or an open. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure greater than the specified value?

5 ohms

Go to Step 32

Go to Step 27

19

Probe the mounting stud for the battery positive cable at the underhood fuse block with a test lamp that is connected to a good ground.

Does the lamp illuminate?

--

Go to Step 32

Go to Diagnostic System Check - Engine Electrical in Engine Electrical

20
  1. Turn OFF the ignition.
  2. Remove the powertrain relay from the underhood fuse block with the J 43244 Relay Puller Pliers. Refer to Relay Replacement In Wiring Systems.
  3. Connect terminal cavity C6 to terminal cavity A5 together at the underhood fuse block with a 20-amp fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Probe the following fuses with a test lamp that is connected to a good ground.
    5. • ETC Fuse
    • ELEK IGN Fuse
    • FUEL INJ Fuse
    • O2 SSR Fuse
    • Emission Fuse

Does the test lamp illuminate on at least one test point of each fuse?

--

Go to Step 21

Go to Step 32

21

Measure the resistance from terminal #85 of the relay to terminal #86 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure within the specified value?

70-110 ohms

Go to Step 22

Go to Step 30

22

Measure the resistance from terminal #30 of the relay to terminal #87 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the DMM display the specified value?

∞ohms

Go to Step 23

Go to Step 30

23

Measure the resistance from terminal #30 of the relay to terminal #85 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the DMM display the specified value?

∞ohms

Go to Step 24

Go to Step 30

24

Measure the resistance from terminal #85 of the relay to terminal #87 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the DMM display the specified value?

∞ohms

Go to Step 25

Go to Step 30

25
  1. Connect a 20-amp fused jumper wire from the battery positive cable at the battery to relay terminal #85. Refer to Using Fused Jumper Wires in Wiring Systems.
  2. Connect a jumper wire from the negative battery cable at the battery to relay terminal #86.
  3. Measure the resistance from terminal #30 of the relay to terminal #87 with a DMM.

Does the resistance measure more than the specified value?

3 ohms

Go to Step 30

Go to Intermittent Conditions

26

Test for shorted terminals and poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 33

Go to Step 31

27

Test for intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 33

Go to Step 31

28

Repair the short to ground in the powertrain relay coil control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 33

--

29

Repair the high resistance or an open in the powertrain relay coil control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 33

--

30

Replace the powertrain relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

--

Go to Step 33

--

31

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 33

--

32

Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.

Did you complete the replacement?

--

Go to Step 33

--

33
  1. Reassemble the vehicle as necessary.
  2. Replace any open fuses.
  3. Turn OFF the ignition for 30 seconds.
  4. Attempt to start the engine.

Does the engine start and run?

--

Go to Step 34

Go to Engine Cranks but Does Not Run

34
  1. Clear the DTC with a scan tool.
  2. Operate the vehicle for 5 minutes.

Does a DTC set during this ignition cycle?

--

Go to Diagnostic Trouble Code (DTC) List

System OK